Shortages of motor fuel have become a periodic occurrence across OPEC member Venezuela, particularly in border regions where smuggling to neighboring countries is common, the result of generous subsidies from state-run oil company PDVSA that have led to nearly-free gasoline.

But this week lines at gas stations in the border states of Zulia and Bolivar were longer than usual, according to Reuters witnesses, and hours-long lines appeared outside service stations in the central states of Aragua and Carabobo. The capital Caracas showed no signs of gasoline shortages.

PDVSA's imports of fuel and diluents, which are mixed with Venezuela's extra-heavy crude, have plunged to 86,000 barrels per day (bpd) on average so far in May, compared with 225,000 bpd for the full month of April, according to internal PDVSA documents and Refinitiv Eikon data.

U.S. sanctions on PDVSA, part of a bid to pressure President Nicolas Maduro to step down, are squeezing government revenue by preventing Venezuela from shipping crude to the United States, previously its largest market.

The sanctions also block U.S. companies from exporting gasoline to Venezuela, prompting PDVSA to import fuel from farther afield.

In addition, Venezuela's 310,000 barrel-per-day (bpd) Cardon oil refinery, operated by PDVSA, halted operations on Wednesday because of damage at some of its units, two workers at the Paraguana refining complex said. It had been operating well below capacity even before the outage.

Cardon is Venezuela's second largest refinery after 645,000-bpd Amuay, which is adjacent to Cardon in Paraguana. As of Wednesday the refinery was processing just 115,000 bpd, one source said, while a second source said it was producing less than 140,000 bpd.

The 187,000 bpd Puerto la Cruz refinery had been offline even before the sanctions were imposed in late January, while the 146,000 bpd El Palito refinery is operating at minimum levels.

Venezuela's refining infrastructure has deteriorated in recent years because of lack of maintenance and investment, prompting the government to import fuel for domestic use. (Reporting by Mircely Guanipa in Punto Fijo and by Marianna Parraga in Mexico City; Additional reporting by Maria de los Angeles in Ciudad Bolivar and Mariela Nava in Maracaibo Writing by Luc Cohen; Editing by Jeffrey Benkoe and Grant McCool)